The invention concerns a universal measuring gauge for geological structures in general, designed in particular for supported mine openings, the construction of which enables the taking of accurate and quick measurements of the spatial orientation of planar and linear geological structural elements not only on free ground, but also in the surroundings affected by a geomagnetic field.
Up to the present, the spatial orientation of planar and linear structural elements has usually been measured by geological compasses of various types.
A disadvantage of the currently employed geological compasses is their unreliable or even entirely incorrect measurements of horizontal strikes (bearings), so-called azimuths, in surroundings affected by disturbing magnetic effects, i.e. in practically all sub-surface mines, prospecting mine openings, communication tunnels, and the like. Further disadvantages are related to the necessity of horizontal setting of the compass during azimuth measurements, and the additional requirement of a new application of the compass during dip measurements by means of the clinometer; the difficulty, unreliability, or even impossibility of measurement, by means of the compass, above the horizon of the operator's eyes, in the roof (hanging wall) of the mine workings, and in narrow joints; as well as the difficulty and considerable inaccuracy of the direct measurement of the spatial orientation of steep-dipping linear elements.
While the geological compass proves satisfactory for geological structural measurements on free ground, where it has become a current tool owing in particular to its small, pocket-size dimensions, its application in surroundings affected by a geomagnetic field proves to be entirely inadequate.
Errors in compass measurements are caused by the deformation of the lines of force of a magnetic field in mine workings, due to the presence of ferromagnetic substances in the form of deposits or rock-forming minerals. These deposits or minerals are characterized by high values of magnetic susceptibility and remanent magnetization, and by the related presence of steel equipment, such as supports, exploitation and transport systems, pipelines, etc., with different remanent magnetization of individual structural parts preserved from the steel-chilling stage, and finally, by the effect of intense electric fields formed in the neighborhood of direct current conductors and power consuming utilities.
As a result of their location, the character of the geomagnetic fields within the mine openings reflects the action of a considerable number of various partial effects subjected to mutual interference. The overall result is either an increase or a decrease of their disturbing effects. This is why such a conspicuous variability has been recorded for the course of lines of force of the locally affected geomagnetic field and the associated changes of the magnetic needle bearings of geologic compasses.
In principle, the simplest device, having measurements independent from the presence of the magnetic field, and thereby enabling one to measure direction angles between structural elements and the axis of the mine opening, is composed of a protractor half-scale with a revolving arm extended to both sides. Measurements by means of this device are based upon a reading of the arm position (which is applied to the measured plane) on the half-scale of the protractor, the diameter of which is situated in the strike (direction) of the axis of the opening. The precision of measurement is limited, particularly on gently dipping structural planes. The strike direction of steep-dipping lineaments is only estimated approximately. The clinometer of the geological compass can also be used for measurements of the dip (inclination) of structural elements.
A more complicated device, based upon similar principles, is the so-called Koark's diopter-goniometer, which has been employed for structural measurements at Swedish magnetite ore deposits-- see H. J. Koark in "Dioptergoniometer fuer Gefuegemessungen im Bereich magnetishcher Erzvorkommen" (Neues Jahrb. Min. Geol., Monatshefte, pp. 169-174, Stuttgart 1951).
The fundamental features of this instrument, applicable only in connection with a theodolite operated by another person, are the half-scale of the protractor, the diameter of which is applied, in horizontal position, to the measured plane; and the revolving arm with levels and two tiny lining rods, normally attached. The strike (direction) of the measured structural plane is calculated (quite intricately) from the geodetically established orientation of the aiming line of the theodolite (situated on a site with good view and aimed at the mutually coinciding lining rods of the diopter-goniometer, their connecting line being identified with the theodolite's aiming line) and the arm position reading on the protractor scale. Broader use of the diopter-goniometer has been prevented by the considerable requirement placed upon operators with regard to specialization and available time.